In order to enhance the competitiveness of the future networks, the Third Generation Partnership Project (3GPP) is researching a new evolved network. A requirement of the evolved network is to implement handover between a 3GPP access system (such as GERAN, UTRAN, or E-UTRAN) and a non-3GPP access system (such as a WLAN or WiMax). In the existing protocol, the handover procedure is implemented via Attach or Tracking Area Update (TAU) procedure by the UE in a new access system.
In the process of developing the present invention, the inventor finds that the processing mechanism of an Attach or TAU process caused by handover differs sharply from the processing mechanism of a normal Attach/TAU process: In a normal Attach process, the network needs to delete all bearers previously created by the user, create a default bearer between the UE and the Packet Data Network Gateway (PDN GW), and register the PDN GW address used by the UE into a Home Subscriber Server (HSS); but in an Attach process caused by handover, the network needs to re-create all bearers previously created by the user. In the normal TAU process, the network does not handle the bearers of the user, but in the TAU process caused by handover, the network needs to re-create all bearers previously created by the user.
In the normal handover between a 3GPP system and a non-3GPP system, the UE is disconnected from the source Access Network (AN) first, and then the UE accesses the target access network through an Attach process. Consequently, the interruption of the UE service is long, which influence the service experience of the user. Therefore, an optimized handover mechanism is adopted for handover between an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) network and a High Rate Packet Data (HRPD) access networks in Code Division Multiple Access (CDMA) network. In the optimized handover mechanism, the user plane path hands over to the target access network first before the UE hands over to the target access network (namely, while the UE is in the source access network).
In the process of developing the present invention, the inventor finds that the UE may hand over from an HRPD network to an E-UTRAN network in either idle state or active state. When the UE performs handover in an active state, the access network may be notified to create the bearer on the access network side in the handover process in order to speed up service recovery time after the UE hands over to the target access network. However, in the idle state, the UE runs no service and is not sensitive to handover delay. Creating bearers on the access network side when the UE is idle is a waste of the access network resources. In a pre-handover mechanism, once the UE handover fails, the UE needs to notify the PDN GW to switch the downlink path back to the source access network. Therefore, the pre-handover mechanism makes the system more complicated.